Time-resolved absorption spectroscopy is used to study the dynamics of protein structural changes subsequent to excitation with short laser pulses. Molecular models for the protein dynamics are used to fit and interpret the measured data. A. The kinetics of ligand binding and conformational changes for sperm whale myoglobin and human hemoglobin (HbA) have been studied following the photodissociation of carbon monoxide from the hemes. Comprehensive sets of data from partial photolysis experiments using polarized excitation permit cooperative and noncooperative processes to be clearly distinguished. These data also provide accurate measurements of the rotational correlation times of these molecules B. The dynamics of short-lived states on the folding pathway of cytochrome c have been investigated using time-resolved absorption spectroscopy. The binding of carbon monoxide destabilized the folded state of reduced cytochrome c, permitting folding to be initiated by photodissociation of this ligand. We have observed transient binding of other at least two different side chains to the heme subsequent to photodissociation of CO. C. We have disassembled, moved, rebuilt and improved all of the instrumentation used by our laboratory.